This invention relates to the mixing of materials to produce a homogeneous mixture. Without prejudice to the generality, the invention is particularly applicable to the mixing of powder or granular materials, e.g. cement and sand, and to the mixing of such materials with a liquid, e.g. plaster with water.
EP 0 255 780-A discloses a method of preparing a homogeneous mixture of powder or granular materials, e.g. sand and cement, with a liquid, in which the materials to be mixed are placed in a bag which is then rolled to tumble the materials.
In EP 0 671 130-A food products are mixed with a condiment by placing the materials into a bag such that the mouth of the bag is suspended from a plurality of bars which move vertically to tumble the contents of the bag.
The present invention seeks to provide a new and inventive method of mixing materials and a new and inventive apparatus for performing the method.
The present invention proposes a method of preparing a homogeneous mixture of two or more materials which comprises:
placing the materials to be mixed into a bag of flexible material;
suspending the bag from an upper region thereof above a plunger; and
producing relative up-and-down movement between the bag and plunger such that the plunger repeatedly moves part of the bag upwardly through the materials contained in the bag to cause mixing thereof.
The invention further provides mixing apparatus comprising:
holding means for suspending a bag from an upper region of said bag;
a plunger located below said holding means; and
means for producing relative up-and-down movement between said holding means and said plunger such that when a bag containing materials to be mixed is suspended from said holding means the plunger repeatedly moves part of the bag upwardly through the materials contained in the bag to cause mixing thereof.
Whilst such relative movement could be produced by moving the bag vertically onto a static plunger, or by moving both the bag and the plunger, it is preferred to move the plunger while the bag remains stationary.
Preferably the amount of relative movement is sufficient to cause the bag to protrude above the mean surface level of the bulk of the material being mixed.
In order to provide an improved mixing action the plunger preferably moves in a non-linear path. It is further preferred to provide for relative rotational indexing between the plunger and the bag with reciprocation of the plunger.
The plunger preferably includes interchangeable heads. A particularly preferred form of head for use in mixing plaster has a leading face which is inclined with respect to the direction of lateral movement of the plunger on its upward stroke. The head preferably includes at least one downwardly inclined facet to increase mixing during downward movement of the plunger.